(1) Field of the Invention
This invention relates to a novel water-soluble resin. In particular, this invention relates to a water-soluble resin for packaging ink, derived from the reaction product of a modified rosin and a bis (secondary amine) such as piperazine.
(2) Description of Prior Art
Resin used as a vehicle for water based packaging ink must exhibit properties such as solubility in water, wet adhesion to polypropylene film, hydrolytic stability, high melting point, and good pigment wetting.
Alcohol soluble polyamide resins have been used extensively in inks for packaging and are commercially available. These polyamides are made from dimerized fatty acids and various polyamines such as ethylene diamine or hexamethylene diamine.
The use of such polyamide resins in ink compositions is described in Floyd, D. E., Polyamide Resins, Reinhold Publishing Co., New York, 1958 and in the Encyclopedia of Polymer Science and Technology, Interscience Publishers, John Wiley Sons, Volume 10, New York, 1969. A typical commercial product is GAX-340 manufactured by Henkel.
For water based ink, a water soluble resin such as acrylic resin or a conventional soluble maleic resin may be used. Acrylic resins have good film properties, but lack adhesion to polyolefin films.
Conventional soluble maleic resins, which contain half-esters, are subject to a certain degree of hydrolytic instability under alkaline conditions. They also lack film toughness.
Water-based ink compositions are disclosed in U.S. Pat. No. 4,963,188 to be prepared by free radical polymerization of rosin and maleic anhydride. Modification of the polymer with an alcohol or an amine prior to utilization in preparing the ink composition is disclosed.
Recently, water soluble resins having qualities of adhesion and wettability for use in packaging ink compositions were developed as the reaction products of rosin modified by Diels-Alder reaction with an .alpha., .beta. unsaturated acid and a compound containing two secondary amine groups, including commercially available piperazine and N,N'-dimethylethylene diamine. These resins are described in parent application Ser. No. 454,416, now patent number 5,066,331.
These resins were developed primarily for use in water/isopropanol-based inks for printing on film, where they perform quite satisfactorily. When using these resins in all-water systems (i.e., no alcohol), it was found that the resin solutions had relatively limited shelf stability. In many cases the solutions gel upon standing for two or three days.
It is therefore an object of this invention to provide improved water soluble resins having qualities of adhesion, wettability and improved stability for us in packaging ink compositions.